Immunohistochemical Characterization of Estrogen and Progesterone Receptors in Lymphoma of Horses

Abstract

Immunohistochemical techniques were used to examine 29 cases of equine lymphoma for estrogen receptor (ER) and progesterone receptor (PR) expression. The lymphomas examined included T-cell-rich large B-cell lymphomas, B-cell neoplasms, and T-cell lymphomas. The individual cases were also classified according to the anatomic location of the tumors. One normal equine lymph node was also examined for ER and PR expression. All of the cases of equine lymphoma and the normal lymph node were negative for Er. A total of 16/29 (55%) PR-positive lymphomas were identified. Seven of the 12 (58%) T-cell-rich large B-cell lymphomas were positive, 7/11 (64%) B-cell tumors were positive, and 2/6 (33%) T-cell neoplasms were positive. Anatomically, 6/9 (66%) subcutaneous lymphomas were PR positive, 3/5 (60%) intrathoracic lymphomas were positive, 1/4 (25%) intra-abdominal lymphomas were positive, 2/5 (40%) intra-abdominal/intrathoracic lymphomas were positive, 1/2 (50%) upper airway lymphomas were positive, and 3/3 (100%) splenic lymphomas were positive. One case involving abdominal and thoracic tumors and leukemia was negative for PR expression. The normal lymph node contained a low percentage (1.9%) of PR-positive lymphocytes. The presence of PR in neoplastic equine lymphoid tissue indicates that these tumors may be responsive to serum progesterone. Also, identification of PR-positive cells in the normal lymph node suggests that PR may be constitutively expressed in normal equine lymphocytes. Further studies are needed to quantify PR levels in normal and malignant equine lymphoid tissue and to determine the usefulness of either progestin or antiprogestin drugs in the management of equine lymphoma.

Equine lymphoma

“…2000). This study also found that the anatomical location of lymphoma correlated with the percentage of neoplastic cells that had progesterone‐positive receptors (100% of splenic lymphomas, 67% of cutaneous, 60% of thoracic, 40% of multicentric and 25% of alimentary of equine lymphomas had progesterone‐positive receptors) (Henson et al . 2000).…”

“…In mares it has been anecdotally reported that the lesions regress during pregnancy but reappear after foaling (Henson et al . 1998; Henson et al . 2000).…”

Clinical, Laboratory, and Histopathologic Features of Equine Lymphoma

“…Previous reports described such receptors on 1 to 10% of tumor cells, but there was no apparent correlation to the hormone produced by an ovarian tumor. 15,16 Thus, the link between hormonal states and neoplastic lymphocyte proliferation or regression remains incompletely understood.…”

“…12,24,34,40 Subcutaneous forms of lymphoma that regress and recur in response to steroid hormone stimulation have been described. 15,16 In these cases, a small proportion of tumor cells expressed nuclear progesterone receptors, which was implicated to account for cell proliferation in response to hormone binding. 16 Characterization of tissues predominantly from abattoir submissions suggested that most horse lymphomas were of B-cell origin and that presence of 40-80% small T lymphocytes was common.…”

“…15,16 In these cases, a small proportion of tumor cells expressed nuclear progesterone receptors, which was implicated to account for cell proliferation in response to hormone binding. 16 Characterization of tissues predominantly from abattoir submissions suggested that most horse lymphomas were of B-cell origin and that presence of 40-80% small T lymphocytes was common. 18 Tumors with such Tlymphocyte infiltrates composed approximately half of all B-cell lymphomas and were classified as T-cell-rich B-cell lymphoma (TCRBCL) because the T lymphocytes were considered to be benign and the B lymphocytes malignant.…”